Sejanus

Lucius Aelius Sejanus (3 June 20 BC-18 October 31 AD) was Prefect of the Praetorian Guard from 14 to 31 AD. He was the right-hand man of Emperor Tiberius for the majority of his reign, and he was used by Tiberius to consolidate his hold on power by murdering his political enemies, including his own son, Drusus Julius Caesar. He was arrested and executed in 31 AD after being accused of conspiring against Tiberius.

Biography
Lucius Aelius Sejanus was born in Volsinii, Etruria, Roman Empire on 3 June 20 BC, and he came from the Roman equestrian class. The son of Lucius Seius Strabo, he was born into the Seii family but he was later adopted by the Aelii by Gaius Aelius Gallus. In 2 BC, Strabo was appointed Prefect of the Praetorian Guard under Emperor Augustus, and Sejanus served under Gaius Caesar during his campaigns in Armenia in 1 BC. In 14 AD, following the death of Emperor Augustus, Empress Livia appointed Sejanus to serve as the new Prefect of the Praetorian Guard, and she sent him to assassinate Agrippa Postumus and Paullus Fabius Maximus, two threats to her son Tiberius' accession to the throne.

Rise to power
Sejanus quickly became Tiberius' trusted advisor, and Tiberius had him elevated to the rank of Praetor. The Roman Senate and the imperial family (especially Tiberius' own son Drusus Julius Caesar) came to dislike Sejanus due to his brutality against political opponents, his cronyism, and his violent rise to power as Tiberius' right-hand man. In 19 AD, he was one of the men behind the poisoning of Tiberius' adoptive son Germanicus in Syria, and Germanicus' widow Agrippina the Elder became involved with a group of senators who were opposed to Sejanus' growing power. In 23 AD, Drusus Julius Caesar struck Sejanus during an argument, feeling jealous that Sejanus had more power than him; Sejanus seduced Drusus' wife Livilla and had Drusus slowly poisoned to death. Tiberius was now forced to leave more administrative matters to Sejanus, but he refused to allow for Sejanus to marry Livilla in 25 AD. Sejanus responded by forcing the emperor into isolation in Campania in 26 AD and then to the island of Capri (where he stayed until his death 11 years later), fueling his paranoia against Agrippina and the Senate. Empress Livia's death in 29 AD left Sejanus with unchecked power, and he purged several senators and wealthy equestrians in Rome, forcing many to commit suicide after show trials. In 30 AD, Sejanus had Agrippina and her sons Nero Julius Caesar and Drusus Caesar starved to death; however, Caligula escaped to Capri in 31 AD.

Downfall
In 31 AD, Sejanus became a Consul of the Roman Empire alongside Tiberius, and he finally became betrothed to Livilla. Senators and equestrians courted Sejanus' favor as if he was emperor, and statues were erected in his honor. However, Antonia Minor discovered letters between Sejanus and Livilla which implicated them in several murders, and Claudius gave Tiberius a letter from Livilla to Sejanus which suggested that he murder Tiberius. At Caligula's suggestion, Tiberius had Naevius Sutorius Macro execute Sejanus, his followers, and his family.